com.gitee.apanlh.util.cache.local.CacheLfu Maven / Gradle / Ivy

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There is a newer version: 2.0.0.2
package com.gitee.apanlh.util.cache.local;

import com.gitee.apanlh.util.base.MapUtils;

import java.util.Iterator;

/**	
 * 	LFU缓存
 * 	
淘汰最少使用次数
 * 	
 * 	@author Pan
 */
public class CacheLfu extends CacheAbstract {
	
	/**	最大容量 */
	private int capacity;
	/** 命中次数 */
	private int hit;
	
	/**
	 * 	默认构造函数
	 * 	
默认256最大容量
	 * 	
	 * 	@author Pan
	 */
	public CacheLfu() {
		this(256);
	}
	
	/**	
	 * 	构造函数
	 * 	
自定义容量
	 * 	
	 * 	@author Pan
	 * 	@param 	capacity 容量
	 */
	public CacheLfu(int capacity) {
		super(MapUtils.newLinkedHashMap(capacity));
		this.capacity = capacity;
	}
	
	@Override
	@SuppressWarnings("unchecked")
	V putHandler(K key, V value) {
		V v = getMap().get(key);
		//	队列不存在记录
		if (v == null) {
			//	如果容量达到上限时移除最小访问次数节点
			if (size() == this.capacity) {
				clearCache();
			}
			return (V) new CacheObject(value);
		}
		//	刷新缓存值并返回
		return (V) flushCache((CacheObject) v, value);
	}
	
	@SuppressWarnings("unchecked")
	@Override
	V getHandler(K key, V value) {
		if (value == null) {
			return value;
		}
		
		hit++;
		CacheObject cacheObject =  (CacheObject) value;
		//	添加访问次数
		cacheObject.setCount();
		return cacheObject.getData();
	}
	
	/**
	 * 	淘汰访问次数最少且最久以前的数据
	 * 	
队列中存在节点数据信息,淘汰访问次数最少的数据
	 * 	
	 * 	@author Pan
	 */
	@SuppressWarnings("unchecked")
	@Override
	public void clearCache() {
		Iterator iterator = values().iterator();
		
		int minCount = -1;
		while (iterator.hasNext()) {
			CacheObject next = (CacheObject) iterator.next();
			int count = next.getCount();
			//	找到访问次数最少的队列数据
			if (minCount == -1 || count < minCount) {
				minCount = count;
			}
		}
		
		if (size() == this.capacity) {
			//	淘汰访问次数最少的数据
			iterator = values().iterator();
			while (iterator.hasNext()) {
				CacheObject cacheObject = (CacheObject) iterator.next();
				int historyCount = cacheObject.getCount();
				//	从队列顶部开始检索访问次数等于检索到的最小访问次数
				if (historyCount == minCount) {
					iterator.remove();
				}
				//	避免清理队尾数据，清理队列顶部一半最小访问次数数据
				if (size() <= (this.capacity / 2)) {
					return ;
				}
			}
		}
	}
	
	/**	
	 * 	刷新缓存值
	 * 	
	 * 	@author Pan
	 * 	@param 	cacheObject	 缓存对象
	 * 	@param 	value		 值
	 */
	private CacheObject flushCache(CacheObject cacheObject, V value) {
		//	如果已存在缓存中更新缓存值
		if (!cacheObject.getData().equals(value)) {
			cacheObject.setData(value);
		}
		//	更新访问次数
		cacheObject.setCount();
		return cacheObject;
	}
	
	@Override
	public String toString() {
		return getMap().toString();
	}	

	@Override
	public int getHit() {
		return this.hit;
	}
	
	@Override
	public boolean equals(Object o) {
		return super.equals(o);
	}
	
	@Override
	public int hashCode() {
		return super.hashCode();
	}
}